1. Field of the Invention
The present invention relates to a suspension device for use in a vehicle seat such as an automotive seat, and in particular to a suspension device having a vertically active elastic element to resiliently support the seat in the vertical direction and a fore-and-aft active elastic element to resiliently support the same in the forward and backward directions.
2. Description of Prior Art
There has been known a suspension device of a vertically and fore-and-aft active type which permits a seat to be resiliently supported in the vertical direction as well as in the forward and backward directions. In general, this sort of suspension device comprises an upper frame, on which the seat is mounted, a lower frame fixed on a floor side of vehicle or automobile, an X-shaped link disposed between the upper and lower frames, a vertically active elastic element provided between the upper ends of the X-shaped link, and a fore-and-aft active elastic element disposed between the lower frame and the floor.
Typically, the vertically active elastic element gives a resilient force to normally bias the X-shaped link in a direction wherein the link is expanded to raise the upper frame, to thereby resiliently support the upper frame relative to the lower frame and absorb a vertical vibration or pitching of the seat, when the automobile is running on a rough road.
On the other hand, the fore-and-aft active elastic element, conventionally, uses a slide member to resiliently retain the lower frame in a given position, allowing the lower frame to be movable forwardly and backwardly to absorb a horizontal vibration or fore-and-aft rolling.
However, in such fore-and-aft active elastic element, the slide member is disposed laterally of the lower frame with a view to securing a wide space between the upper and lower frames, sufficient for the X-shaped link to be contracted at the lowest possible level. As a result, such slide member and associated parts are projected from the opposite sides of the lower frame to make greater the whole size of the suspension device, requiring thus a wide space in the cabin for installation thereof. Further, the slide member needs to be formed from a rigid material, as with the upper and lower frames, to support both suspension device and seat, which means to increase unexpectedly the weight and size of the slide member per se, rendering complicated its structure. Then, this particular conventional suspension device is disadvantageous in the assemblage, costs and the range of its applicability to small sized automobiles.